1. Field
This disclosure relates to sensor systems for detecting concealed objects and particularly to systems that use an infrared sensor in combination with a millimeter wave illumination source.
2. Description of the Related Art
Passive video and infrared sensor systems typically capture images of scenes or subjects using natural or ambient illumination. Such sensors can capture high resolution images, but do not have the ability to detect concealed objects, such as weapons and explosive devices hidden beneath a person's clothing. Active sensors, such as microwave radar systems, may have the ability to penetrate clothing, but generally do not provide sufficient image resolution to attempt to identify specific concealed objects.
An active infrared sensor system is, to some extent, a hybrid of an infrared sensor and a radar system. An active infrared sensor uses an infrared sensor to detect localized temperature variations induced when a subject is illuminated by an electromagnetic energy source. Active infrared sensors using high power microwave illumination have been proposed for detecting buried objects such as land mines (see, for example, U.S. Pat. No. 6,343,534 B1; U.S. Pat. No. 6,753,529 B2). Active infrared sensing using millimeter wave illumination has also been proposed for longer range applications which may include concealed object detection (Hubbard et al., Long-Range Thermal Imaging Using A Millimeter-Wave Source, 33rd International Conference on Plasma Science, Jun. 4-8, 2006).
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having a reference designator with the same least significant digits.